Estudios comparativos de la lepidosis supra-ocular en Squamata (Reptilia) y su relacion con la taxonomia evolucionaria.

• Autor: Cei, Jos

RESUMEN

Observaciones morfológicas previas sobre un gran número de especies permiten establecer una correspondencia entre la peculiaridad de los patrones sistemáticos de las escamas supraoculares de Squamata y la posición evolutiva de cada taxón considerado en los cladogramas propuestos por Estes et al. (1988). Aparte del significado biológico general de estos hallazgos, incluso para discutidas orientaciones taxonómicas, la lepidosis supraocular llega a refrendar una decisión sistemática con su evidencia. Así, en Iguania, la familia Leiosauridae, propuesta por Frost et al. (2001), aparece sostenida hasta en el detalle de su división en las subfamilias Leiosaurinae y Enyaliinae. Siempre en Iguania Pleurodonta se evidencian ejemplos como los inconfundibles patrones de escamas supraoculares de Opluridae, Leucocephalidae, Polychrotidae, Tropiduridae. A nivel específico la interdependencia en Iguanidae de los géneros Iguana, Cercosaura, Brachylophus, Conolophus, puede llevar a postular pretéritos acontecimientos paleogeográficos. También amerita énfasis la llamativa separación, según este criterio morfológico, entre Iguania y Scleroglossa, la uniforme lepidosis de centenares de Gekkota, o la excepcional fisonomía de Autarchoglossa, en sus ramas tan individualizadas de Scincomorpha (Lacertoidea; Teiioidea; Scincoidea) o Anguimorpha.

Palabras clave: diagnosis, escamas supraoculares, patrón específico lepidosis, Pleurodonta, Squamata, taxonomía

COMPARATIVE STUDIES OF SUPRAOCULAR LEPIDOSIS IN SQUAMATA (REPTILIA) AND ITS RELATIONSHIPS WITH AN EVOLUTIONARY TAXONOMY

SUMMARY

Former observations on characteristic patterns of supraocular scutellation in different specific or supraspecific taxa of Squamata are extended and analyzed in this general critical review. A relationship between a defined morphological supraocular iepidosis in a particular taxon and its evolutionary position in a classificatory system, such as the cladograms obtained by Estes et al. (1988), was tested and confirmed. Supraocular scales of Squamata are not morphological elements at random, but can be assumed as morphological scale characters, useful in systematic comparative examinations and able to strengthen some discussed new systematic assessments, such as the family status of Leiosauridae and its subfamilies in Pleurodont Iguanians, proposed by Frost et al. (2001), as well as in several other cases.

Key words: Squamata, supraocular scutellation, specific lepidosis pattern, diagnosis, Pleurodonta, taxonomy

INTRODUCTION

The selection of significant somatic morphological characters (shape, size, structure) will play an essential role in providing a systematic herpetological arrangement, at least to species level: furthermore it can apply also to more elevated ranks of the herpetological classification. We are pointing out here some interesting aspects of the so-called lepidosis, or cutaneous scale covering of Reptilia, mainly in Lacertilian lizards. More exactly, the differentiated scales bilaterally located in the supraocular region of the head, bounded inside by the orbital semicircles, and by the ciliary eye border outside (Figure 1). Given the noticeable position of these supraocular scales in the head scutellation of Squamata, their presence has generally been reported in many diagnostic descriptions of species. Nevertheless, no true emphasis was ever placed on their peculiar taxonomic significance: either as ah important generic characteristic structure of the dorsal head lepidosis, or as distinctive supraocular patterns in separated systematic groups, from different genera to families and higher categories. A preliminary paper was provided on this matter (Cei, 2003), dealing with supraocular scales in species and genera of Iguania, as well as in some far-away taxonomic categories, such as Scleroglossa Teiid lizards. Thus, considering the remarkable number of past and recent species descriptions, a detailed review and discussion of such a noticeable but still disregarded anatomical peculiarity could be a very interesting job, postulating a distfibution pattern not at random but in agreement with the phylogenetic subdivisions of well-known modern classificatory essays.

[FIGURE 1 OMITTED]

Some isolated reports about specific supraocular scutellation in Reptiles, besides a preliminary paper (Cei, 2003), deal with circumorbitals in one row or in two rows between supraoculars and median head shields, as emphasized in Frost's (1992) taxonomic revision of Tropidurus groups of lizards that points out discrimination among the genera Uranoscodon, Microlophus, Plesiomicrolophus and Tropidurus. Likely in Etheridge's (1970) comparative research the systematic differences in supraciliaries were suitably applied to discriminate Plica and Uranoscodon from other members of the Tropidurus groups. However, apart from these interesting but limited citations, a whole zoological discussion and critical valuation of lacertilian supraocular scutellation is yet wanting to our knowledge. The present work will attempt to reach better and conclusive information on such a suggestive and little analyzed subject.

MATERIAL AND METHOD

Given the aim of this work, its outcome is a detailed representation of the postulated relationships between the supraocular scutellation patterns and the taxonomic categories of Squamata. Our comparative graphic documentation, exposed in Figures, was mainly obtained from careful observations and drawings of preserved specimens, or in some case from careful adaptations of controlled reproductions by reliable authors. The available materials above all have been the specimens of a personal collection (JMC-DC: José M. Cei Diagnostic Collection), occasionally complemented by past studies of species from the Herpetological Collections of some Museums or Scientific Institutions whose list and acronyms are following. IBA-UNC: Collections of the Instituto de Biología Animal, Universidad Nacional de Cuyo, Mendoza, Argentina; MZUSP: Museo de Zoologia, Universidade de São Paulo, Brasil; MCZ: Museum of Comparative Zoology, Harvard University, Cambridge, USA; NMNH: National Museum of Natural History, Smithsonian Institution, Washington, USA; FMNH: Field Museum of Natural History, Chicago, USA; MNHN Paris: Museum Nationale Histoire Naturelle, Paris; UNNE: Universidad Nacional del Nordeste, Corrientes, Argentina.

Given the Figures including the total samples drawn that support our present report and discussion, a separated list of the examined specimens would be prolix and unnecessary. Moreover the general localities of samples were opportunely indicated in the Figures. When it was necessary, morphological details of the lizards were drawn under a dissecting microscope. Peter's Dictionary (1964) was a reference for morphological and anatomical nomenclature, as well as the several Etheridge's papers, i.e. his Ctenoblepharis adspersa redescription (1995). The drawings of the Figures have been all more or less slightly magnified: we believe that individual magnification of symbols in every identified drawing scale is useless to our purposes. Besides the specimens documented in the Figures, hundreds of specimens corresponding to the patterns have been observed and compared, for improving the truthfulness and significance of our samples.

Among the most important literature supporting the harvesting, arranging and discussion of our representative samples, we wish to highlight the useful, good or outstanding papers or reviews by Anderson (1999), Angel (1942), Blarc (1977), Brygoo (1971, 1978), Dixon (1973), Donnelly and Myers (1991), Greer (1970), Grismer et al. (1994), Haas and Werner (1969), Halliday and Adler (2002), Hoogmoed (1973), Kluge (1974), Leviton et al. (1992), Mertens (1958, 1959), Pregill (1992), Ruibal (1964), Savage (1963), Tayer (1956), Van Demburg (1978), Vanzolini et al. (1965, 1980) and Wiens (1993).

RESULTS

Analytical review of comparative reports on supraocular lepidosis in Squamata

As pointed out in the Introduction, the aim of this research was to put in evidence a correlative relationship between a classificatory system and a significant set of data on supraocular scutellation in Squamata reptiles. The phylogenetic indented taxonomy exhibited in the valuable conclusive statements by Estes et al. (1988) was considered asa suitable model (Figure 2), together with the reassessment of Iguania by Frost et al. (2001). Such taxonomy has been followed here for comparison with our detailed morphological observations, far away from any aprioristic personal opinion. Then, without disregarding other interesting systematic contributions, as the recent paper by Schulte et al. (2003), in full agreement with our findings, we recognize the taxon Pleurodonta and its included families as in the mentioned Frost et al. 's (2001) arrangement. On the contrary, the opposite general taxon Iguanidae (sensu Boulenger, 1895) postulated in the paper by Schulte et al., based on bio-molecular and morphological researchs, is fully discordant with our results.

In the following 27 Figures, specific supraocular scutellation patterns belonging to genera and families of the major taxa listed in the indented taxonomy are reported. Evidently it was impossible to check the thousands of living species of lizards, but significantly representative drawings of enough generic and specific taxa, are provided.

[FIGURE 2 OMITTED]

Two opposed major systematic categories stand out in the Squamata indented taxonomy: Iguania and Scleroglossa, sustained by anatomical, mostly osteological characters. Acrodonta and Pleurodonta are a subdivision of Iguania, likewise countersigned by osteological differences. We can anticipate that a fairly simple supraocular scutellation belongs to Acrodonta, but a remarkable variety of differentiated supraocular scales is shown by the Pleurodonta families.

Agamidae and Chamaeleonidae are two large and widespread Acrodont families. With more than 50...